Whisk the marinade ingredients together in a bowl. Place the sliced portobello mushrooms in a large plastic bag and pour the marinade into the bag. Zip the bag up and shake the bag to get all the mushrooms coated in the marinade. Place the bag in the fridge for a few hours to allow the mushrooms to soak up all the spices.

In a large skillet coated with non-stick cooking spray, olive oil or water, sauté the sliced onions until translucent. Add in the bell peppers and sauté for about 5 more minutes. Lastly add in the mushrooms and marinade and sauté until the mushrooms have softened.

Serve the pepper and mushroom mixture warm over tortillas with salsa, guacamole and cilantro.